watchdog: stm32_iwdg: Add pretimeout support

The STM32MP15xx IWDG adds registers which permit this IP to generate
pretimeout interrupt. This interrupt can also be used to wake the CPU
from suspend. Implement support for generating this interrupt and let
userspace configure the pretimeout. In case the pretimeout is not
configured by user, set pretimeout to 3/4 of the WDT timeout cycle.

Signed-off-by: Marek Vasut <marex@denx.de>
Reviewed-by: Clément Le Goffic <clement.legoffic@foss.st.com>
Tested-by: Clément Le Goffic <clement.legoffic@foss.st.com>
Reviewed-by: Guenter Roeck <linux@roeck-us.net>
Link: https://lore.kernel.org/r/20240415134903.8084-1-marex@denx.de
Signed-off-by: Guenter Roeck <linux@roeck-us.net>
Signed-off-by: Wim Van Sebroeck <wim@linux-watchdog.org>

drivers/watchdog/stm32_iwdg.c

@@ -18,6 +18,7 @@
 #include <linux/module.h>
 #include <linux/of.h>
 #include <linux/platform_device.h>
+#include <linux/pm_wakeirq.h>
 #include <linux/watchdog.h>
 
 #define DEFAULT_TIMEOUT 10
@@ -28,6 +29,7 @@
 #define IWDG_RLR	0x08 /* ReLoad Register */
 #define IWDG_SR		0x0C /* Status Register */
 #define IWDG_WINR	0x10 /* Windows Register */
+#define IWDG_EWCR	0x14 /* Early Wake-up Register */
 
 /* IWDG_KR register bit mask */
 #define KR_KEY_RELOAD	0xAAAA /* reload counter enable */
@@ -47,22 +49,29 @@
 #define SR_PVU	BIT(0) /* Watchdog prescaler value update */
 #define SR_RVU	BIT(1) /* Watchdog counter reload value update */
 
+#define EWCR_EWIT	GENMASK(11, 0) /* Watchdog counter window value */
+#define EWCR_EWIC	BIT(14) /* Watchdog early interrupt acknowledge */
+#define EWCR_EWIE	BIT(15) /* Watchdog early interrupt enable */
+
 /* set timeout to 100000 us */
 #define TIMEOUT_US	100000
 #define SLEEP_US	1000
 
 struct stm32_iwdg_data {
 	bool has_pclk;
+	bool has_early_wakeup;
 	u32 max_prescaler;
 };
 
 static const struct stm32_iwdg_data stm32_iwdg_data = {
 	.has_pclk = false,
+	.has_early_wakeup = false,
 	.max_prescaler = 256,
 };
 
 static const struct stm32_iwdg_data stm32mp1_iwdg_data = {
 	.has_pclk = true,
+	.has_early_wakeup = true,
 	.max_prescaler = 1024,
 };
 
@@ -88,27 +97,35 @@ static inline void reg_write(void __iomem *base, u32 reg, u32 val)
 static int stm32_iwdg_start(struct watchdog_device *wdd)
 {
 	struct stm32_iwdg *wdt = watchdog_get_drvdata(wdd);
-	u32 tout, presc, iwdg_rlr, iwdg_pr, iwdg_sr;
+	u32 tout, ptot, presc, iwdg_rlr, iwdg_ewcr, iwdg_pr, iwdg_sr;
 	int ret;
 
 	dev_dbg(wdd->parent, "%s\n", __func__);
 
+	if (!wdd->pretimeout)
+		wdd->pretimeout = 3 * wdd->timeout / 4;
+
 	tout = clamp_t(unsigned int, wdd->timeout,
 		       wdd->min_timeout, wdd->max_hw_heartbeat_ms / 1000);
+	ptot = clamp_t(unsigned int, tout - wdd->pretimeout,
+		       wdd->min_timeout, tout);
 
 	presc = DIV_ROUND_UP(tout * wdt->rate, RLR_MAX + 1);
 
 	/* The prescaler is align on power of 2 and start at 2 ^ PR_SHIFT. */
 	presc = roundup_pow_of_two(presc);
 	iwdg_pr = presc <= 1 << PR_SHIFT ? 0 : ilog2(presc) - PR_SHIFT;
 	iwdg_rlr = ((tout * wdt->rate) / presc) - 1;
+	iwdg_ewcr = ((ptot * wdt->rate) / presc) - 1;
 
 	/* enable write access */
 	reg_write(wdt->regs, IWDG_KR, KR_KEY_EWA);
 
 	/* set prescaler & reload registers */
 	reg_write(wdt->regs, IWDG_PR, iwdg_pr);
 	reg_write(wdt->regs, IWDG_RLR, iwdg_rlr);
+	if (wdt->data->has_early_wakeup)
+		reg_write(wdt->regs, IWDG_EWCR, iwdg_ewcr | EWCR_EWIE);
 	reg_write(wdt->regs, IWDG_KR, KR_KEY_ENABLE);
 
 	/* wait for the registers to be updated (max 100ms) */
@@ -151,6 +168,34 @@ static int stm32_iwdg_set_timeout(struct watchdog_device *wdd,
 	return 0;
 }
 
+static int stm32_iwdg_set_pretimeout(struct watchdog_device *wdd,
+				     unsigned int pretimeout)
+{
+	dev_dbg(wdd->parent, "%s pretimeout: %d sec\n", __func__, pretimeout);
+
+	wdd->pretimeout = pretimeout;
+
+	if (watchdog_active(wdd))
+		return stm32_iwdg_start(wdd);
+
+	return 0;
+}
+
+static irqreturn_t stm32_iwdg_isr(int irq, void *wdog_arg)
+{
+	struct watchdog_device *wdd = wdog_arg;
+	struct stm32_iwdg *wdt = watchdog_get_drvdata(wdd);
+	u32 reg;
+
+	reg = reg_read(wdt->regs, IWDG_EWCR);
+	reg |= EWCR_EWIC;
+	reg_write(wdt->regs, IWDG_EWCR, reg);
+
+	watchdog_notify_pretimeout(wdd);
+
+	return IRQ_HANDLED;
+}
+
 static void stm32_clk_disable_unprepare(void *data)
 {
 	clk_disable_unprepare(data);
@@ -207,11 +252,20 @@ static const struct watchdog_info stm32_iwdg_info = {
 	.identity	= "STM32 Independent Watchdog",
 };
 
+static const struct watchdog_info stm32_iwdg_preinfo = {
+	.options	= WDIOF_SETTIMEOUT |
+			  WDIOF_MAGICCLOSE |
+			  WDIOF_KEEPALIVEPING |
+			  WDIOF_PRETIMEOUT,
+	.identity	= "STM32 Independent Watchdog",
+};
+
 static const struct watchdog_ops stm32_iwdg_ops = {
 	.owner		= THIS_MODULE,
 	.start		= stm32_iwdg_start,
 	.ping		= stm32_iwdg_ping,
 	.set_timeout	= stm32_iwdg_set_timeout,
+	.set_pretimeout	= stm32_iwdg_set_pretimeout,
 };
 
 static const struct of_device_id stm32_iwdg_of_match[] = {
@@ -221,6 +275,40 @@ static const struct of_device_id stm32_iwdg_of_match[] = {
 };
 MODULE_DEVICE_TABLE(of, stm32_iwdg_of_match);
 
+static int stm32_iwdg_irq_init(struct platform_device *pdev,
+			       struct stm32_iwdg *wdt)
+{
+	struct device_node *np = pdev->dev.of_node;
+	struct watchdog_device *wdd = &wdt->wdd;
+	struct device *dev = &pdev->dev;
+	int irq, ret;
+
+	if (!wdt->data->has_early_wakeup)
+		return 0;
+
+	irq = platform_get_irq(pdev, 0);
+	if (irq <= 0)
+		return 0;
+
+	if (of_property_read_bool(np, "wakeup-source")) {
+		ret = device_init_wakeup(dev, true);
+		if (ret)
+			return ret;
+
+		ret = dev_pm_set_wake_irq(dev, irq);
+		if (ret)
+			return ret;
+	}
+
+	ret = devm_request_irq(dev, irq, stm32_iwdg_isr, 0,
+			       dev_name(dev), wdd);
+	if (ret)
+		return ret;
+
+	wdd->info = &stm32_iwdg_preinfo;
+	return 0;
+}
+
 static int stm32_iwdg_probe(struct platform_device *pdev)
 {
 	struct device *dev = &pdev->dev;
@@ -255,6 +343,11 @@ static int stm32_iwdg_probe(struct platform_device *pdev)
 	wdd->max_hw_heartbeat_ms = ((RLR_MAX + 1) * wdt->data->max_prescaler *
 				    1000) / wdt->rate;
 
+	/* Initialize IRQ, this might override wdd->info, hence it is here. */
+	ret = stm32_iwdg_irq_init(pdev, wdt);
+	if (ret)
+		return ret;
+
 	watchdog_set_drvdata(wdd, wdt);
 	watchdog_set_nowayout(wdd, WATCHDOG_NOWAYOUT);
 	watchdog_init_timeout(wdd, 0, dev);